external wastegate sizes....

[Sydneykid]

Good questions Dr....

Quote:

Surely it's not just a matter of open / closed???

Wouldn't the amount the gate has to open be a cruital factor as it will need to flow varying volumes to maintain a set boost level across a certain RPM range??

The wastegate responds to boost pressure. The more boost pressure on the diaphragm and it's spring, the further the valve opens. Ignoring early opening for a minute. If your target boost is 1.5 bar, when it the actual boost gets to 1.51 bar, the valve should open a little tiny bit. Now we all know that doesn't happen, the boost goes up so fast it flies past 1.5 and the valves opens vary fast. If the valve is too big, it lets too much exhaust gas bypass the turbine, boost drops fast and the valve closes. Then boost climbs rapidly again because the valve is closed. Valve opens and the cycle starts again.

With the correctly sized wastegate with the exactly same spring rate, the valve will open just as far but it is smaller and so will bypass less exhaust. Thus it may not completely shut again. If it is correctly sized it should not have bypassed way too much exhaust gas, maybe only a little too much. So the valve just moves a little more open and closed to control the boost.

Secondly it's a lighter valve (remember a 35 mm valve head is 50% of the weight of a 50 mm valve head) so it has less inertia and can open and close faster.

Quote:

As for the varying 0,3 bar... could that not be caused due to a poorly setup or inappropriate boost controller?

Well that's what I thought, so I replaced the wastegate spring with one of the right rate for the target boost ie; no AVCR. Same result, fluctuating boost. So I used one of the Autospeed boost control systems (they always work for me), still with the right spring rate in the wastegate. Same result. So we changed the turbo to another with a slightly less aggressive compressor. Better, but not much.

It was at this stage I suspected the 60 mm wastegate was too big for 230 rwkw. But I couldn't convince the owner, he believed and was continually told by everyone he spoke to, that bigger was always better. So I recommended that the guys put on a smaller wastegate (35 mm) with the original turbo and not tell him. Bingo no boost fluctuations.

Oh, and it never lost 1 rwkw from the smaller wastegate, but it picked up a noticeable amount of response. This happened with another car (it had a heap more problems as well) and that's when I started thinking about a formula to pick up ridiculously (small or large) sized wastegates. Save a lot of time and money chasing other stuff.

[DoughBoy]

My eyes hurt :cry:

[Scooby]

  Sydneykid said:

It’s all about empowerment, so you (the Skyline owner) can sift out the BS.

Absolutely.

Thanks SK.

[BOOSTD]

do me do me..... 280rwkw @20psi

[Sydneykid]

  BOOSTD said:

do me do me.....  280rwkw @20psi

Yo BOOSTD, the formula was about empowering you, as the Skyline owner, not about me doing calcs for everyone. Oh OK, but just this once;

280 rwkw = ~450 bhp

450 bhp / 11 = 41 lbs of airflow = 41 mm wastegate

Now if you want to run 20 psi, then that's statistically the most likely sized wastegate.

I can't say as I've ever seen a 41 mm wastegate, so the choice is 40 mm or 45 mm. For good response, personally I would go with the 40 mm wastegate. The reasons are in the previous posts.

Hope that helps

[BOOSTD]

much appreciated...I feel the empowerment now

for interest sake ATP turbo recommend a 38mm wastegate for this power level.

[Sydneykid]

  BOOSTD said:

much appreciated...I feel the empowerment now

for interest sake ATP turbo recommend a 38mm wastegate for this power level.

Pretty close, did they tell you why 38 mm? The brand of wastegate they suggested, did it have a 40 mm size?

No tricks, I am just trying to find out the background info to help my understanding.

[BOOSTD]

They sell Tial. And yes they also supply a 40mm item....

[Sydneykid]

  BOOSTD said:

They sell Tial. And yes they also supply a 40mm item....

Cool, thanks

[Craved]

some absolutely awesome info there SK, definately cleared the subject up for me totally (within reason)

at least now i know what the theory is in this decision while im out there shopping!!!

[benm]

coming to a bookstore near you, "Sydneykid Engines: 101"

I think I learnt something..... the rest went right over my head.

[Guest Moses]

how does he get the time to write all that?

*imagines monkey typing while SK dictates from his recliner smoking a cigar*

Thanks for info, useful to me too!

[Craved]

LOL - too true can picture that

[Sydneykid]

  Moses said:

*imagines monkey typing while SK dictates from his recliner smoking a cigar*

Nah tried the monkey, types OK but butt ugly :thumbdwn: . I find the wench :boobs: much better.

Dictating from the recliner is OK, but I am not into cigars, I prefer a glass of red instead, :alcoholic

[Lithium]

Preferring to dig up an old post than to start a semi-redundant topic - if I was was to aim for in the 400-500hp @ flywheel rangewith an RB25DET, running 1-1.1bar with a T3/T04E with .7 turbine A/R, do you think around ~40mm external (8psi spring) would be sensible?

Cheers in advance

[Sydneykid]

  Lithium said:

Preferring to dig up an old post than to start a semi-redundant topic - if I was was to aim for in the 400-500hp @ flywheel rangewith an RB25DET, running 1-1.1bar with a T3/T04E with .7 turbine A/R, do you think around ~40mm external (8psi spring) would be sensible?

Cheers in advance

500 bhp = 45 lbs per minute of airflow

45 lbs per minute of airflow= 45 mm

You are not going to get 500 bhp with 1.1 bar out of a RB25DET, I suspect something like 1.6 bar would be more like it

So 45 / 1.6 X 1.4 = 39.4 mm

A 40 mm wastegate would be OK

400 bhp = 36 lbs per minute of airflow

36 lbs per minute of airflow= 36 mm

I suspect something like 1.3 bar would be the boost required to make that power

So 36 / 1.3 X 1.4 = 38.8 mm

A 40 mm wastegate would be OK

As for the wastegate actuator spring rate, I wouldn't go below 12 psi as it gives much better boost control when the boost controller (whatever type) has less work to do, to fill the gap between the target boost and the spring rate.

You should check the compressor map for your turbo to make sure my guesses for power and boost are accurate. Hope that helps:cheers:

[Lithium]

  Sydneykid said:

500 bhp = 45 lbs per minute of airflow

45 lbs per minute of airflow= 45 mm  

You are not going to get 500 bhp with 1.1 bar out of a RB25DET, I suspect something like 1.6 bar would be more like it

So 45 / 1.6 X 1.4 = 39.4 mm

A 40 mm wastegate would be OK

400 bhp = 36 lbs per minute of airflow

36 lbs per minute of airflow= 36 mm  

I suspect something like 1.3 bar would be the boost required to make that power

So 36 / 1.3 X 1.4 = 38.8 mm

A 40 mm wastegate would be OK

As for the wastegate actuator spring rate, I wouldn't go below 12 psi as it gives much better boost control when the boost controller (whatever type) has less work to do, to fill the gap between the target boost and the spring rate.

You should check the compressor map for your turbo to make sure my guesses for power and boost are accurate.  Hope that helps:cheers:

Thanks

Yeah I know 500hp won't be a number I'd see on 1.1bar ~1bar is a shorter term aim - but I'd like to set 500hp in my sights (turbo would be capable of it) so want to change as little as possible when I decide to raise boost levels.

Admittedly I wasn't sure if 8psi would be too low or not. Truth be told, the motivation for having such a broad power range etc, is I've actually been FORCED to buy a new turbo as my R33 one failed, and would like to move forward but will only really be able to get it running with FMIC, ECU and the turbo and wastegate as well as stock fuel system - so run it on low boost initially and gradually bump up the pressure as I get more supporting mods with 500hp as a an option if I decide I want to crack the motor open.

The concern I have is that the factory fuel system wouldn't be able to supply for 12psi on that kind of turbo, or do you think I'd be safe?

[Sydneykid]

  Lithium said:

Yeah I know 500hp won't be a number I'd see on 1.1bar ~1bar is a shorter term aim - but I'd like to set 500hp in my sights (turbo would be capable of it) so want to change as little as possible when I decide to raise boost levels.  This is why I set such a broad power range....

Admittedly I wasn't sure if 8psi would be too low or not.  Truth be told, the motivation for having such a broad power range etc, is I've actually been FORCED to buy a new turbo as my R33 one failed, and would like to move forward but will only really be able to get it running with FMIC, ECU and the turbo and wastegate as well as stock fuel system - so run it on low boost initially and gradually bump up the pressure as I get more supporting mods with 500hp as a an option if I decide I want to crack the motor open.

The concern I have is that the factory fuel system wouldn't be able to supply for 12psi on that kind of turbo, or do you think I'd be safe?

OK Lithium, that fills in the gaps, it is always easier to make suggestions when you know the whole story. The 12 psi wastegate actuator spring may well be too high. You really should refer to your compressor map as it depends on the airflow that turbo develops at 12 psi. I have a number of T04E maps, what trim is the compressor? I have 40, 46, 50, 54, 57 and 60.

[Lithium]

The one I was looking at was a 50 trim - but I found out that its actually a Stone Mountain (aka. dodgey quality). I am on the look out at the moment, I spotted this for sale but suspect it might be a bit much - 60trim comp. on it....

http://www.trademe.co.nz/Trade-Me-Motors/C...on-18846258.htm

[Craved]

OOOHHHH SK do you have any maps that describe the HKS GT 3040 with .70AR and 1.12 exhaust??

im thinking they wouldn't be obtainable... but since this thread is back i thought id ask as my turbo system is going in very soon!